1. Field of the Invention
This invention relates to sensor rationality diagnostics, more particularly, it relates to emission or exhaust control systems of internal combustion engines and apparatuses, systems, and methods for diagnosing functionality of temperature sensors associated with exhaust aftertreatment catalyst/filter systems. More specifically the invention relates to apparatuses, systems, and methods for verifying in-range thermistor rationality in exhaust aftertreatment catalyst/filter systems.
2. Description of the Related Art
Catalyst/filter aftertreatment systems for diesel particulate matter are designed to catch particulate matter or soot in diesel particulate filter (DPF). The DPF over time becomes filled with the particulate matter and must be cleaned. One method of cleaning a DPF is by burning off the accumulated particulate through the use of a diesel oxidation catalyst (DOC).
A DOC is a flow through device containing a honeycomb like substrate coated with a precious metal such as platinum or palladium. The catalyst interacts with the exhaust as it passes through the DOC, raising the temperature of the exhaust and causing the particulate matter to burn. The combination of a DPF and a DOC in an exhaust aftertreatment system for diesel particulate matter has been used to prevent harmful pollutants from entering the atmosphere.
Diesel particulate matter combusts at temperatures above 500 degrees Celsius. As particulate matter combusts, additional temperature increases may be seen. These high temperatures may be above the temperature at which the filter material maintains its structure. Temperature sensors have been used to monitor temperatures in diesel exhaust aftertreatment systems utilizing DOCs and DPFs. The sensors are often thermistors which provide varying degrees of electrical resistance depending on the temperature in which they are operating. The information provided by the sensors is used to diagnose potential problems in the aftertreatment system and also to control efficient regeneration of the DPF.
According to government regulations, heavy-duty engines produced in 2007 and subsequent model years are required to be equipped with an Engine Manufacturer Diagnostic (EMD) system. The EMD system must be capable of monitoring emission systems to detect malfunctions and notify the operator of such malfunctions. Where determined by the engine manufacturer to be feasible, the EMD system must detect malfunctions of input components such as thermistors on the emission system. In particular, in-range rationality refers to detecting temperatures within the operating range of the system which are not rational for the particular operating condition of the engine or exhaust aftertreatment system.
Example methods used to test exhaust gas temperature thermistors for rationality include a key-on diagnostic which compares the thermistor readings to engine coolant temperature, intake temperature or engine temperature to see if there is a gross difference between the temperatures measured. The key-on diagnostic must compare exhaust temperatures with systems unrelated to exhaust, and is suited to find temperature sensor readings that are grossly in error, but not sensors which are offset from the true temperature reading.
Another method, called a dither, looks at whether the thermistor temperatures are changing over time. According to this method, temperatures are measured over a long period of time to determine whether the temperature reading is stuck at one point. This method is not able to detect sensors which are offset from the true temperature but changing accurately as the temperature changes.
The current invention can replace or be used in conjunction with previously developed thermistor rationality diagnostics and is applicable to all vehicle platforms and existing aftertreatment systems. It can also be configured for any type of sensor—pressure, flow, etc.—in a wide range of applications. The diagnostic can be used with all products with catalyst elements and at least three temperature sensors. The current invention provides a method, system and apparatus for diagnosing thermistors which are stuck within range as well as thermistors which are offset.
From the foregoing discussion, it should be apparent that a need exists for a thermistor diagnostic which is applicable to all vehicle platforms and uses existing aftertreatment systems components. The diagnostic must be compatible with all products with catalyst elements and temperature sensors. The diagnostic must be able to diagnose thermistors which are stuck within range as well as thermistors which are offset from the true temperature reading.